Exhaust gas from car engines lately has been required to be purified as much as possible for release into the air in view of preventing air pollution. For this reason, an exhaustion system provided with a catalytic converter purifies exhaust to harmless gas. In this case, the temperature of the catalysts has to be measured exactly to increase purification efficiency, i.e. catalyst efficiency. Consequently, temperature sensor elements to measure the temperature of exhaust from car engines need to be heat-resistant, thermal shock resistant, heat-responsive and reliable.
FIG. 35 shows an example of a temperature sensor element comprising a composite of sintered body 100 and lead 101 of precious metal. Sintered body 100 exhibited a reponse property of linear type, nonlinear type, negative type or positive type with respect to temperature. FIG. 36 shows temperature sensor 120. Lead 101 from temperature sensor element 102 was connected with lead 103. Metallic housing 105 was provided on the outer face of lead 103 through electric insulator 104. The other end of housing 105, where no sensor element was provided, was fixed on metallic flange 106. Flange 106 is to fix the sensor on substances whose temperature is to be measured. Electric-insulator 107 insulated lead 103, housing 105 and flange 106. Cap 108 made of heat-resistant metal covered temperature sensor element 102 (e.g. JP Kokai Laid-Open No. Hei 6-283310, and U.S. Pat. No. 5,497,139).
However, when conventional temperature sensors having a temperature sensor element as described above were installed to catalyst converters of cars, the temperature sensors had some problems. The temperature sensors were not heat responsive. The manufacturing process was complicated. That was because temperature sensitive body 100 was a sintered body and therefore the size and thermal capacity were large, and further because temperature sensor element 102 was covered with cap 108 of heat resistant metal. When heat resistance and shock-proofing tests were performed using the conventional temperature sensor having no cap 108 of heat resistant metal, temperature sensitive body 100 cracked.
To solve the above problems, the invention aims to provide a temperature sensor element superior in heat-resistance, thermal shock resistance, heat-response and reliability, where the resistance hardly changes over time, a temperature sensor having such a temperature sensor element and a method for producing the element.